Wooden sailing ships were extremely vulnerable to fire. Modern ships are not exempt either, and in submarines it can be really catastrophic. The Kursk was sunk by a fire in the torpedo room, for an example.

Wooden ships were (& are) the some of the biggest firetraps ever invented. They are composed of wood (dried, with pitch soaked rope used as caulking) with canvas sails & tarred rope stays (the mobile rope rigging was not tarred but still flammable). This is why “red hot shot” was invented and used against them from shore based forts. (It was _never_ used in ship vs. ship combat–no one was ever foolish enough to fire up a furnace to heat shot on a wooden ship in the middle of a battle.) (Never say “never”, someone will come up with the appropriate obscure reference! But, if it was ever done, it was vanishingly rare!)

So, this being considered, using Napalm, thermite, white phosphorus, and other incendiary compounds against them is feasible. A MAJOR concern is safely manufacturing and storing these compounds until used. However, this cannot be an insoluble problem as the Byzantines stored the ingredients for Greek Fire on their galleys for nearly a thousand years without a major catastrophe. (probably in amphorae – large clay urns, stored point down in sand bins) So if you can figure out safe storage & handling, go for it. A flame thrower using napalm would be the closest thing to resurrecting Greek Fire that you could come up with.

That said, the sailors of the wooden ship days were certainly NOT unaware of the dangers, ships crews were very well drilled in firefighting, as they lived in these tinderboxes – and smoked tobacco there, too!

Dry rot is frequently encountered in the wooden parts of ships above the waterline. This is an ongoing fight for wooden ships.

Firefighting drills and equipment were standard, especially in the Royal Navy and US Navy. Sand barrels, and water barrels were carefully distributed around the ship, and maintained. Various pumps could be employed for firefighting, as well as draining the bilges. The precautions taken in the blackpowder magazines included keeping the candle lanterns on the outside of a door with an oiled paper window to isolate the flame from stray grains of powder. This usually worked…

In combat, wooden vessels sit in water, and their sails were frequently soaked in water. Burning a boat is a non-trivial exercise. You can add the difficulty we have, in getting major wooden beams to do more than surface-char. It can be seen in burnt-out Brick Buildings, with major wooden beams as part of the interior structure. It can be seen in a fireplace, when a too-large chunk of log be placed in the fire. It is why we work so hard, with axe & hatchet, to reduce logs to split-logs, and split-logs to kindling, and feather-shave some of the straight-grained kindling into starter-sticks.

Look at pictures of the remains of a forest-fire. All the big trees are still standing, though scorched. Many of the smaller trees are burnt, complete.

There are some arguments about the efficacy of fire as a weapon against wooden ships:

A good beginning is to attempt to find _any_ ships destroyed by fire during major naval battles, and to count the number destroyed by fire during normal sailing, vs. the number sank in other ways.

This needs to be researched for a definitive answer, but some well known examples of the use of incendiary weapons in sea battles:

Sir Francis Drake vs. the Spanish Armada – fireships

We suspect the Fire Ships did their job due to the combination of the thorough soaking in combustibles (accelerants in arson speak – liquid fuels), and the Powder Magazine on board, which would throw burning chunks all over any ships still anchored. The threat of having a floating bonfire close aboard, combined with the threat of it exploding, was enough to make most Captains cut their anchor(s) free, for to flee. There are similar problems today when a lumberyard catches fire…

First used against the Turks during the Greek war of independence. The exploding shells set the wooden ships afire quite readily and took care of the damage control crews at the same time. It wouldn’t take a large amount of guns to destroy a large warship with the use of shell.

Now, we come down to a why question, before we go deeper into the how of the thing.

Why destroy a valuable ship, just because some unfriendly types are using it to harass you? Why not take it away from them?

Cripple the rigging, and the ship becomes unmaneuverable. Blow the officers off of the quarterdeck, and the rest of the crew might just change sides. These were very real calculations in the days of sail – and why things like chain or LaGrange shot were used against rigging, and grape and canister shot against both rigging and crews.

And why boarding parties got called away – ships were valuable, especially under the English prize system.

The international nature of the crews were profound. You didn’t have nationalism as we know it today – so appealing to patriotism doesn’t work. Crews (especially pressed men) were considered the lowest of the low. English recruitment from Cheapside slums and/or impressments by the “Press Gang”. No national navies as such in the 1630s. There are navies – but philosophically quite different in makeup from even the Napoleonic times, let alone the later 1800s.

Even then, it is interesting to study sea chanteys (var. chanties, shanties) and find that English chanteys were widely used by Dutch, French, Russian, and all Baltic Sailors, sometimes with the lyrics changed into a patois!

So – turning coats, turning privateer or just disappearing are very real factors in the type of tactics used. Esprit de Corps is not a complicating factor in the 1630s.

OK, so we’ve determined that yon 74 is a determined nasty, and her crew will take her down with them. She must be destroyed so that trade can be resumed, and more importantly, so that the Captain of the Port can resume his customary afternoon siestas!

Dry wood, and tarred hemp rope and canvas sails could all be made to burn with a little effort. The theory behind heated cannonballs was that they would get hotter than just what the forces involved with shooting could induce, thus possibly igniting sails, or timbers if lodged in the woodwork.

An accurate, and hopefully long-ranged delivery method is needed for the incindiary materials.

Thermite is extremely effective, if you can safely deliver it without killing yourself with a pre-mature ignition, and assuming that your fusing then goes off on or just before impact.

Napalm has similar issues, but you can light the fuse prior to launching from a catapult or coehorn mortar such as a bomb ketch would use. You will need multiple strikes to overwhelm the bad guys’ damage control parties, though…

White phosphorous is a bitch to make, and extremely nasty as an incindiary. Definitely needs a SAFE time or impact fuse.

Black powder as a bursting charge is not much of an incindiary. can happen if a hot fragment sparks off a fire though.

Napalm, Fugasse, or Greek Fire have been used in naval conflicts going back to at least Greco-Roman times. (Greek Fire is pine tar (pitch) mixed with sulfur, quicklime (NOT slaked lime or milk of lime!), and if you have it, saltpeter)

Archimedes was known to have developed a projector – think prototypical flamethrower – used to defend Syracuse against Roman invaders. It’s rumored that he took his responsibilities as a Hoplite very seriously, and got himself killed by a legionnaire who had orders to capture him in reasonably good health…

The good news about flamethrowers is that they are line-of-sight, subject to air resistance and gravity limiting their range. That leads to the downside, you need to get within range to ensure several hits for a sure kill.

If there were no damage control, then a 1/2 liter of napalm could burn out a wooden ship.

In the real world, with motivated damage control parties, figure about 20 liters, widely distributed.

We could go on, but hopefully this has encouraged a discussion of the topic, and a consideration that it isn’t necessarily the best or easiest way to take out a wooden ship.

Especially due to the risks to the defenders in making and delivering the incindiary devices. Kids, DO NOT try this at home!!! It can & probably WILL hurt you…

Some questions:

1. Would fire would be particularly dangerous against wooden ships? Stories suggest that it would be. The fact that they would take the trouble to heat cannon balls red hot also suggests that it would be.

Unattended fire can be dangerous. A blaze once started is hard to put out. Starting that blaze is the hard part. The crew know all about fire and they like their ship just the way it is (Not burning). They will attempt to stop the blaze from starting.

In a combat situation, this means dampening down the hull and rigging (A bit like throwing water onto the road… It does not mean water logged. Just damped down so sparks can’t catch.

It doesn’t matter which of the above. In sufficient quantity, they will all do the job.. Delivery can be a problem.

3. How much would be needed? Someone said that 1 liter of napalm would not be enough. I used to start bonfires with gasoline and 1/2 liter was plenty.

Right. That 1/2 liter was poured onto dry timber and allowed to soak in. The wood tended to be broken up so that some of it could easily catch fire. Try pouring your 1/2 liter over a 12″ log and see if it’ll catch fire (Good sound timber.) Now try again after first wiping with a damp rag…

If there were no damage control, then a 1/2 liter of napalm could burn out a wooden ship.

In the real world, with motivated damage control parties, figure about 20 liters, widely distributed.

It may or may not catch. I’m guessing. Not.

4. How should it be delivered? Cannon, rocket, bomb, mortar, howitzer, catapult, other? I thought that a cannon ball filled with thermite would be much easier to handle than a red hot cannon ball, and would get much hotter, and be nearly impossible to put out.

What are you going to make your thermite cannon ball out of? But if you could prepare and fire one into the hull of an enemy ship.. It could start a fire. But as soon as the thermite is burnt, good old water can put the fire out. And they can control the fire around the thermite with sand and water.

Meanwhile.. How are your people coping with enemy cannon balls coming into your crew spaces. Especially as your crews get the next thermite/napalm – WP cannonball ready? Of course, this also applies to the damage control parties as well. Cannon fire is pretty much an equal opportunity problem…

Remember.. If it goes off inside your ship, YOU have troubles. The inside of a ship is usually much drier than the outside, and more likely to catch fire (Still not that easy, but easier than outside.)